The present invention relates to a motor driving device suitable for driving a brushless DC motor, which is employed in e.g., an air-conditioner, air cleaner, hot water supply, and information apparatus such as a copy machine, printer, optical medium apparatus, and hard disc apparatus. It also relates to a motor driving device suitable for driving an induction motor and a reluctance motor and the like. More particularly, it relates to a motor driving device that can substantially reduce torque ripples, vibrations and noises of the motor in operation. The present invention also provides an apparatus including the same motor driving device.
A brushless DC motor is widely used as a driving motor of an air conditioner and an information apparatus because of its advantages such as a long service life, high reliability, and simplicity of speed control. FIG. 9 is a circuit diagram of a conventional motor driving device, and FIG. 10 shows signal waveforms at respective sections of the circuit shown in FIG. 9 with respect to motor rotating angles (electrical angle).
As shown in FIG. 9, a driving device for the brushless DC motor (hereinafter referred to as simply xe2x80x9ca motorxe2x80x9d), in general, detects a rotor position with a plurality of position detectors 901, 903 and 905 which are formed of Hall elements. Three-phase distributor 890 receives position signals Hu, Hv and Hw from the position detectors, and outputs three-phase distributing signals UH0, UL0, VH0, VL0, WH0 and WL0. These signals are modulated by pulse width modulator (PWM) 840 into signals having a pulse width responsive to set-signal S prepared by speed setter 860. Gate driver 830 controls six switches, forming power feeder 820, to switch on or off sequentially based on output signals from modulator 840 and output signals from three-phase distributor 890. Power feeding to three-phase coils 811, 813 and 815 disposed to a stator is thus sequentially switched responsive to a rotor position, such as signals U, V, W shown in FIG. 10, thereby rotating the motor. FIG. 11 shows torque generated in the motor.
The torque shown in FIG. 11 is described hereinafter. If we direct our attention to phase-U coil 811, differential signal U-N between signal U and neutral point signal N is applied to coil 811. Signal U-N is a rectangular wave signal as shown in FIG. 11. When back electromotive force of phase-U coil 811 shapes in a sine wave such as signal Ue, the torque due to coil 811 is roughly proportional to the product of signal U-N multiplied by signal Ue, and the torque becomes what is shown by torque Tu in FIG. 11. In the same manner, the torque due to phase-V coil 813 and phase-W coil 815 become what are shown by torque Tv and Tw. Torque generated in the entire motor is thus torque xe2x80x9cTallxe2x80x9d that is the sum of the torque of respective phases.
Torque xe2x80x9cTallxe2x80x9d has a certain size of ripple as shown in FIG. 11. This torque ripple causes vibrations while the motor is driven, and the vibrations can resonate with the apparatus in which the motor is mounted, thereby producing noises. The vibrations also prevent the apparatus from being finely controlled, which blocks the performance of the entire apparatus from improving.
The present invention addresses the problem discussed above and aims to provide a simply structured motor driving device that can restrain torque ripples, vibrations and noises generated while a motor is driven. This motor driving device can also drive an object with higher power and in a higher efficient manner.
The motor driving device of the present invention comprises the following elements:
a motor having three-phase driving coils;
a wide-angle feeding device for feeding power to respective phase-coils in a width of 150xc2x0 electric angle; and
a controller for controlling an amount of power to be fed to the respective phase-coils by the wide-angle feeding device.
The wide-angle feeding device can detect overlapping periods in which adjacent two coils out of three coils stay in the same fed condition. The controller controls an amount of power to be fed during the overlapping periods as a first amount and another amount of power to be fed during the other periods than the overlapping periods as a second amount.
This structure discussed above allows the motor driving device of the present invention to reduce substantially the torque ripples, vibrations and noises of the motor in operation.